2025-12-08 – Weekly Hydrology News : Groundwater overdraft: GRACE vs wells

Last week in our hydrology community, discussions were vibrant and varied. Members focused on the practical applications and regulatory implications of PFAS, MS4, and WOTUS, with a keen interest in accredited professional development hours. The comparison between SUMMA+mizuRoute and WRF-Hydro sparked technical debates, particularly concerning model performance at short lead times. Additionally, there was a deep dive into groundwater overdraft detection, focusing on the relative effectiveness of GRACE satellite data versus well measurements.


This Week’s Hot Topics

Accredited PDHs on PFAS, MS4, and WOTUS
This discussion highlights the importance of staying current with environmental regulations. It’s a valuable resource for those seeking PDHs in these critical areas.
Read more here

SUMMA+mizuRoute vs WRF-Hydro at 6-hr lead
A technical comparison of two hydrologic models, focusing on their predictive accuracy. It’s a must-read for modelers working on short-term forecasts.
Read more here

What flags overdraft first, GRACE or wells
This thread examines the effectiveness of different methods for detecting groundwater depletion, a critical issue for sustainable water management.
Read more here

Keeping storm grab samples defensible
Focusing on ensuring data integrity, this discussion offers practical tips for maintaining the quality of stormwater samples.
Read more here

Fastest route for a spill to a well
An analysis of spill dynamics, this conversation is crucial for understanding and mitigating risks to water supplies.
Read more here

Faster flood runs without losing accuracy
Exploring ways to optimize flood modeling, this topic is ideal for those looking to enhance computational efficiency without compromising results.
Read more here


Looking forward to another week of engaging discussions and professional growth. Stay curious and connected.

I’ve had GRACE vs wells line up only after removing GLDAS soil moisture + reservoir storage from TWS and bias-correcting GRACE to the pre-2015 well median; otherwise irrigation-season pumping makes GRACE look too jumpy… If the basin’s small or karstic this can backfire, but for Central Valley–scale work the JPL mascons are a solid starting point: https://grace.jpl.nasa.gov/data/.

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Quick tip: I reconcile GRACE with wells by fitting only the cool-season median to avoid irrigation transients, then compute GWS = TWS − (soil moisture + SWE + surface water) with JPL RL06M mascons and scale factors https://grace.jpl.nasa.gov/data/get-data/jpl_global_mascons/. Building on @emma.clarke56, bias-correcting to a pre-2015 well baseline helps, but I’ve found a simple “winter-only” quantile mapping works just as well when reservoir releases are quirky. Caveat: if canals or bank storage dominate, subtract observed reservoir/canal storage explicitly or you’ll chase ghosts.

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